Non-isothermal evaporation type heat transfer apparatus

ABSTRACT

1,126,265. Cooling systems. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 7 July, 1966 [7 July, 1965], No. 30495/66. Heading F4U. A cooling system comprises an enclosure containing a vaporizable liquid and having one wall which is adapted to be exposed to a source of heat, internal projection on said one wall, means for sub-cooling the liquid so that vapour formed adjacent the projections will condense in the body of liquid and elastic means exposed to the liquid for damping pressure fluctuations caused by the vaporization and condensation process. As shown, an annular enclosure 3 surrounds a cylinder 1, e.g. the anode or collector of an electron discharge tube or the cylinder of an I.C. engine, having projections 5, the liquid in the enclosure is sub-cooled by a coil 6 and the elastic means comprises a partly inflated flexible annular body 20. A screen 21 and a filling hole having a stopper 10 are provided. The liquid may be sub-cooled externally of the enclosure (Figs. 5 and 6, not shown) and the screen may be perforated (Fig. 6). The cylinder to be cooled may be closed at one end and the surrounding enclosure bell-shaped (Figs. 1, 7 and 10, not shown). The elastic means may be partspherical and contained in either the enclosure (Fig. 1) or in a sub-chamber screwed into the filling hole in place of the stopper (Fig. 2, not shown); the sub-chamber may alternatively contain a flexible diaphragm (Fig. 3, not shown). In further embodiments (Figs. 7 and 10) the elastic means comprises a vapour pocket at the top of the enclosure. Formulµ for determining the configuration of the internal projections are given.

y 1968 c. A. BEURTHERET 3,384,160

NON-ISOTHERMAL EVAPORATION TYPE HEAT TRANSFER APPARATUS Filed June 28, 1966 4 Sheets-Sheet l y 21, 1933 c. A. BEURTHERET 3,384,160

NON-ISOTHERMAL EVAPORATION TYPE HEAT TRANSFER APPARATUS Filed June 28, 1966 4 Sheets-Sheet 2 M y 1958 c. A. BEURTHERET 3,

NONISOTHERMAL EVAPORATION TYPE HEAT TRANSFER APPARATUS Filed June 28, 1966 4 Sheets-Sheet 5 May 1968 c. A. BEURTHERET 3,334,150

NON-ISOTHERMAL EVAPORATION TYPE HEAT TRANSFER APPARATUS Filed June 28, 1966 4 Sheets-Sheet 4 5a 4 b2 H United States Patent 3,38%,i60 NON-ISOTHERMAL EVAPORATION TYPE HEAT TRANSFER APPARATUS Charles A. Beurtheret, Saint-Germain-en-Laye, France,

assignor to Compagnie Francaise Thomson Houston- Hotchkiss Brandt, Paris, France iled June 28, 1966, Ser. No. 561,131 Claims priority, application France, July 7, 1965,

3,8 2 19 Claims. (Cl. 165-74) AESTRACT 6F THE DISCLOSURE This invention relates to heat transfer apparatus of the kind utilizing the evaporation of a vaporizable liquid to dissipate the heat from one surface of a Wall having heat applied to its opposite surface.

The applicant has disclosed in :a number of prior patents and co-pending patent applications, evaporation heat transfer apparatus of this general class, wherein the heat transfer efiiciency was greatly increased over prior such apparatus through the provision of extensions or protuberances on the wall surface exposed to the vaporizable liquid. These protuberances resulted in the establishment of stable temperature gradients over the side surfaces of the protuberances, so that the temperature at the root of the protuberances was considerably higher than the ap-ices of the protuberances projecting into the surrounding liquid. The heat-dissipating wall surface was, therefore, nonisot'herm, in marked contrast with the isotherm heat dissipating surfaces that were deliberately maintained in earlier evaporation heat transfer structures.

It was found that through the use of such heat dissipating protuberances it was possible to operate the heat transfer structures at considerably higher temperatures, and therefore with considerably higher heat dissipation rates and heat transfer efliciencies, than had been possible with the earlier, isotherm, heat dissipating surfaces, without the danger of occurrence of local hot spots conducive to destructive burn-out of the metal constituting the heat dissipating wall. A detailed theoretical explanation of the phenomena involved may be found, for example, in applicants Patent No. 3,235,004, and the theory will be but summarized here.

Briefly then, it can be said that in the isotherm heat dissipating, surfaces that were used prior to the applicants research, the temperature of the surface had to be held to a value lower than a so-called critical temperature, which could be determined for each particular liquid and each particular operating temperature from the so-called Nukiyama curve relating to the liquid. The critical point for water at atmospheric pressure, for example, was about 125 C. Whenever it was attempted to exceed a certain critical heat flux, an unstable or run-away condition would ensue in which the temperature of the wall was at any time liable to leap suddenly to an enormously higher temperature, such as from the said 125 C. to more than 1000 C. in the case of water at atmospheric pressure, resulting in destructive burnout of the metal.

3,384,160- Patented May 21, 1968 With the non-isotherm heat dissipating surfaces including grooves or channels between extensions of the wall, as disclosed in the applicants said earlier patents, on the other hand, the stable temperature gradients established along the sides of the extensions encompassed the critical point, with the root temperatures of the protuberances being substantially higher, and the apical temperatures substantially lower, than said critical temperature. It was found that owing to the temperature stabilizing effect thus produced, it was feasible to operate the heat dissipating structure so that the temperature of the surface at the roots of the extensions could be durably held at values substantially higher than the so-called critical value, without any tendency for the temperature at any point to run away and produce metal burnout. Much higher heat transfer rates could thus be safely achieved.

The applicants non-isotherm heat transfer structures have in the past years received various industrial applications, chief among which has been the cooling of the anodes and collectors of high-power electron discharge tubes, such a television transmission tubes, klystrons, and the like. Due to the considerable increase in power rating which the improved coolers have made possible, the applicants non-isotherm coolers (known by the registered trademark Vapo-tron), have virtually replaced all earlier cooling devices in that application Vapotron concept has likewise been applied to the cooling of internal combustion engine cylinders, as Well as chemical and nuclear reactors.

In the applicants earlier non-isotherm (Vapotron) heat transfer structures, the large vapor bubbles for-med by the nucleate boiling of the vaporisable liquid adjacent to the protuberances were, at least in part, led off from the heat dissipating surface and evacuated together with the liquid out of the boiler and into condensing means external to the boiler in which the vapor was recondensed to liquid for recirculation through the boiler past the heat dissipating surface. The present invention stems partly from a recognition, by the applicant, that the said earlier non-isotherm heat transfer structures could have their operating efiiciency even further increased if the recondensation of the vaporized liquid, instead of taking place outside the boiler, could be made to occur within the body of vaporizable liquid at a relatively small distance from the heat-dissipating surface and its extensions. In other words, it was found desirable to apply to the applicants non-isotherm (Vapotron) evaporation heat transfer structures, the concept known as surface or local boiling.

Quoting from the standard work by William H. McAdams, Heat Transmission, McGraW-Hill Book Co., 3rd edition, p. 389, Surface or local boiling is a form of nucleate boiling which occurs when a liquid at a temperature below saturation is brought into contact with a metal surface hot enough to cause boiling at the surface of the heater. The vapor bubbles condense in the cold liquid, and no net generation of vapor is realized with degassed liquid. Extremely high film coeflicients and peak fluxes may be obtained; hence local boiling is advantageous in high-duty applications.

In theory, surface boiling can quite easily be induced in an evaporation cooling system simply by maintaining the over-all temperature of the vaporizable liquid at a value sutficiently lower than the saturation temperature of the liquid at the pressure used in operation, i.e. subcooling the liquid. Such subcooling can be produced in either of two principal ways: (1) circulating the liquid through the boiler at a suificiently high flow velocity, or (2) providing a secondary heat exchanger, such as a cooling coil through which a secondary coolant is circulated, in the boiler, in which case the body of main or primary vaporizable liquid can be maintained stationary in the boiler.

When it was attempted, however, to induce surface boiling and recondensation of the vapor bubbles in the boiler of a non-isotherm evaporation cooler according to the applicant's earlier structures, by either of the two subcooling techniques just outlined, an unexpected difliculty was encountered, at all but comparatively low heat dissipation rates. The operation became noisy and irregular, with loud, repeated impacts occurring in the boiler. The applicants investigations showed that this was due not to the actual bullition, process but to the large and rapid pressure fluctuations created by the repeated process of vaporisation and reeondensation within the boiler. The situation was objectionable not only because of the noise itself, inacceptable in many installations, but because the sharp pressure fluctuations of which the noise was an indication and which are believed to attain many atmospheres in amplitude, cause cavitation and suction extremely detrimental to the stability of the boiling process. It is a chief object of this invention to eliminate this difficulty.

Objects of this invention, therefore, are to provide improved evaporation heat-dissipating structures of the non-isotherm type, whose operating efliciency and heat dissipating capacity are yet further increased; to provide such structures in which the liquid is subcooled to recondense the vapor substantially immediately as it is formed, and which will nevertheless operate smoothly and silently; to provide non-isotherm heat dissipating or cooling apparatus capable of operating at very high dissipating rates, using a body of vaporizable liquid under substantial static pressure, and yet silent and smooth in operation; to provide such structures that can operate satisfactorily in any attitude with respect to the vertical, i.e. upright, oblique, horizontal, or inverted, as well as being operable in the absence of a gravitational field. Other objects will appear.

In accordance with a chief aspect of the invention, a non-isotherm heat dissipating structure wherein the heat dissipating surface is provided with heat-dissipating extensions or protuberances in accordance with the applicants earlier teachings, is used in conjunction with a body of vaporisable liquid in contact with said surface, which in operation is subcooled to a temperature substantially lower than the saturating temperature of said liquid at the pressure of operation. As a consequence, the vapor bubbles vaporized adjacent said protuberances are caused to recondense in the subcooled liquid substantially as said bubbles are formed. Further means are provided in pressure-transmitting relation with said liquid in the enclosure adapted for elastic contraction and expansion in response to pressure fluctuations created by said vaporization and recondensation effects, whereby substantially to damp out such fluctuations.

The elastically expansible damping means may, in one embodiment, comprise at least one recessed member made of rubber-like sheet material partly inflated with gas, which may resemble a partly deflated balloon, arranged in the enclosure. In another embodiment, the expansible damping means may comprise a flexible diaphragm mounted to have one side exposed to the liquid in the enclosure and its other side exposed to a body of gas at suitable pressure. In yet another embodiment, the expansible damping means may simply comprise a vapor pocket arranged to be maintained in operation in an upper portion of the enclosure above the liquid therein.

Exemplary embodiments of the invention will now be described with reference to the accompanying drawing, wherein:

FIG. 1 is a simplified view in axial cross section showing heat dissipating structure according to the invention as used for cooling the anode of a high-power electron tube, and including a stationary body of vaporizable liquid together with a secondary heat exchanger in the form of a cooling coil to subcool said liquid;

FIG. 2 is a partial view in section showing a modification;

FIG. 3 similarly shows a further modification;

FIG. 4 is a view generally similar to FIG. 1 wherein the elastically expansible damping means of the invention is differently shaped (in the form of a toroid) and is differently positioned;

FIG. 5 is a generally similar view of an embodiment wherein the body of vaporizable liquid is continuously circulated through the boiler to provide for the desired subcooling effect;

FIG. 6 shows a modification of the embodiment of FIG. 5;

FIG. 7 is a simplified view in axial section of an embodiment in which the elastically expausible damping means is provided as a pocket of vapor collecting in the top of the boiler;

FIGS. 8 and 9 relate to the prior art, and illustrate in partial cross section two preferred forms of construction of the heat dissipating protuberances in accordance with the applicants earlier Patent No. 3,235,064 and copending application Ser. No. 512,090 filed Dec. 7, 1965, respectively, and

FIG. 10 illustrates 'an embodiment of the invention which constitutes a preferred modification of the embodiment shown in FIG. 7.

In the embodiment of FIG. 1, the reference it designates a heated object that is to be cooled by means of the heat-transfer apparatus of the invention. The object 1 is by way of illustration shown as comprising the anode of a high-power electron tube, and is in the form of a recessed, generally cylindrical body closed at its upper end. The internal components of the tube are not here shown, and may include the usual high-temperature cathode from which electrons are emitted towards the inner surface of the anode 1, as well as any number of conventional control electrodes and the like. The inner surface of the anode 1 is thus, in operation, heated by the electron bombardment at a very high rate, and this heat is dissipated by the apparatus of the invention, now to 'be described.

The heat dissipating apparatus comprises a base 2 in the form of a flat disk surrounding the base of the anode structure 1 and sealingly secured around the anode periphery by a brazed or other suitable joint. Mounted on the base 2 is a bell shaped cover 3 having its bottom periphery brazed or otherwise sealingly secured to the upper periphery of base 2 and defining a sealed boiler chamber thereover and around the anode 1. The bell cover 3 is provided with a filling aperture in its top sealed by a screw plug 10. In use, the boiler cavity is filled through said aperture with a body 9 of suitable liquid, usually distilled water.

Positioned within the boiler cavity defined by bell 3 is a cooling coil 6 of conventional type, in the form of a helically Wound tube of suitable heat conductive metal such as copper, here shown as having two internested helical sections coaxially surrounding the periphery of anode 1. The extremities of the tubular coil 6 are led out through the sidewall of bell 3 to provide an inlet 7' and an outlet 8 for circulating a cooling liquid through the coil, from a conventional fluid circulating system not shown. The cooling coil 6 thus constitutes a secondary heat exchanger serving to impart energetic cooling to the body of primary heat exchange fluid 9. By circulating a secondary cooling liquid through coil 6 at an appropriately high flow rate, it is possible to keep the generally stationary body of primary liquid 9 contained within the boiler chamber at a temperature below saturation i.e. to subcool said liquid. Under these conditions, the vapor bubbles generated in the liquid 9 in the vicinity of the intensely hot surface of anode I, are made to reconden'se within the relatively cool liquid 9 immediately as they are formed, and there is no net generation of vapor in the body of liquid 9. Such a condition is termed surface boiling or local boiling and is known to be capable of producing comparatively very high heat dissipation fluxes.

The application of surface or local boiling conditions as just described, while a fairly recent development in industrial heat transfer apparatus, is not per se novel. Cooling devices using a surface boiling liquid have been constructed and have operated satisfactorily prior to this invention. However, such surface-boiling coolers of the prior art have generally been used for the cooling of heated surfaces having substantially isotherm temperature chara-cterstics, whereas in the present invention the surface-boiling cooler illustrated and above described is applied to the cooling of a non isotherm surface, as will now be described.

The outer surface of the anode 1 is shown formed with an array of outwardly projecting extensions, protuberances or ribs 5. As disclosed in 'a number of applicants prior patents and co-pending applications, some of which are identified elsewhere herein, such extensions or protuberances when appropriately dimensioned, have the remarkable property of stabilizing the temperature over the heat dissipating surface. Intense temperature gradients become established over the side surfaces of the protuberances 5, so that these surfaces will include temperatures both below and above the so-called critical temperature at which, in the absence of such continuous temperature gradient, the temperature would tend to run away to excessively high values leading to local burnout of the metal. Thus the provision of the protuberances 5 imparts a non-isotherm characteristic to the heat dissipating surface, with a number of high, stable temperature gradients present thereover, and as explained in the aforementioned patents and applications as a consequence of this characteristic it becomes possible to operate the cooling system at very much higher temperatures and greater heat fluxes without danger of burn-out, than was possible in the absence of the protuberances. While these earlier devices according to applicants earlier patents had a cooling efficiency greatly superior to that of comparable devices lacking the temperature-stabilizing protuberances, it appeared desirable to achieve even higher heat dissipating rates and cooling efliciencies through an operative combination of the applicants non-isotherm heat dissipating surfaces with the surface boiling concept described above. Difiiculties were encountered however.

At the greatly increased heat dissipating rates made possible by the temperature-stabilizing protuberances, on an average of five to ten times higher than the highest rates safely attainable with the isotherm type surfaces, large masses of vapor form within the channels between the protuberances 5, and these great bubbles must be rapidly recondensed by a very energetic subcooling of the liquid 9 from the secondary cooling coil 6. These conditions tend to create sharp, rapid, fluctuations of pressure within the body of subcooled liquid especially in a closed container, with consequent shocks and noise of a level that cannot be tolerated in most installations. The sharp pressure variations also lead to cavitation, i.e. momentary suction which is detrimental to the stability of the complex evaporation process.

In accordance with the present invention, it has been found that these objectionable effects can be practically eliminated through the provision of elastically expansible damping means within the boiler enclosure, capable of taking up the rapid pressure variations produced.

As shown in FIG. 1, the expansible damping means is provided in the form of one or more recessed elements such as 12 made of a suitable flexible material such as natural or synthetic rubber sheet, containing a sealed body of gas therein, e.g. air. The expansible members 12 may be in the form of balloons initially inflated to a pressure substantially less than the desired operating pressure. In

operation, the high pressure peaks momentarily produced on partial vaporization of the liquid 9 will cause the elements 12 to collapse partly and then reexpand as the vapor bubbles recondense in the liquid. The elements 12 thus operate to damp the pressure fluctuations, and it is found that such damping action is sufficient to ensure smooth and satisfactory operation of the cooling system. Heat dissipating rated considerably higher than those achievable with any cooling arrangement according to the prior art are thus successfully achieved. Representative performance figures of system according to the present invention will be indicated later herein.

It will be evident from the above description of the cooling system of FIG. 1 that the body of primary cooling liquid 9 therein is continually maintained under substantial pressure, and that the necessary heat exchange contact between said liquid 9 .and the heat input and output surfaces 4 and 6 respectively, is herefore at all times ensured. As a result such a sytem can be operated at any desired orientation to the vertical, and also in the absence of any gravitation field, as aboard a spacecraft or satellite. In such cases, it may be desirable to provide means (not shown in FIG. 1) for positively holding the expansible damping elements 12 in a part of the boiler spaced from the heat transfer surfaces so that they shall not substantially interfere with the convection movements of the liquid 9 near said surfaces.

The inflated expansible damping means 12 shown in FIG. 1 may be generally spherical or may be toroidal, and may be loosely attached to the upper dome-shaped part of the boiler shown in FIG. 1 as by means'of one or more suitable collars, or otherwise.

One convenient means of maintaining the expansible damping means away from the heat exchange surfaces without interfering with its expansion and contraction as required for the operation of the invention, .is shown in FIG. 2. In this modification, the filling aperture at the top of the boiler bell 3 is made somewhat wider than what is shown in FIG. 1, and the solid screw plug 10 of that figure is replaced with a recessed screw plug 13. A generally spheroidal inflated damping balloon 11 is shown positior ed within the recess of the plug, and is prevented from escaping out of that recess into the main body of liquid 9 by means of a perforate grid or the like as shown at 14 positioned across the base of the recessed plug.

In the modification shown in FIG. 3, the expansible damping means comprises a spherical two-part attachment consisting of a lower hemisphere 15 and an upper hemisphere 15. The lower hemisphere member 15 is provided with an externally screw threaded bottom orifice 18 adapted to be screwed into an internally threaded orifice formed in the boiler bell 3, e.g. in place of the screw plug 10 shown in FIG. 1. The upper hemisphere member 16 is provided with a plugged orifice 19 for introducing pressure gas, e.g. air, into the upper part of the appliance as will presently become apparent.

The hemisphere members 15 and 16 are flanged at their mating peripheries, and a flexible diaphragm 17 has its periphery sealingly clamped between the flanges. In operation with the appliance fixed in place the region below diaphragm 17 is filled with the liquid 9 from the body of primary cooling liquid filling the boiler. The region above membrane 17 is filled with a gas, e.g. air, at a pressure somewhat less than the prescribed operating pressure, by way of the orifice 19 which is subsequently plugged. The movements of the diaphragm 17 will then serve to damp the pressure fluctuations within the boiler in a manner similar to that described for the inflated elements 11 and 12 in FIGS. 1 and 2. It will be observed that the damping appliance illustrated in FIG. 3 is structurally very similar to a shock-absorber of the so-called hydropneumatic (or oil-air) type sometimes used in automobile construction. It has in fact been found that such an automotive shockabsorber .as found on the current market can be used as the damping means in a cooling system according to the present invention, with only minor modifications. In some cases involving low pressurisation, the outer hemisphere 16 may be open to the atmosphere or may be altogether omitted.

In the embodiment of the invention shown in FIG. 4, the boiler enclosure 3 is in the form of an annular casing secured around the turface of the tubular body 1 that is to be cooled, which in this case extends completely through the boiler enclosure. The hot body while it may be the anode or collector of a high-power electron discharge tube as in FIG. 1 is here assumed to be a cylinder of an internal combustion engine. Heat-dissipating protuberances 5 are provided. Boiler casing 3 has a plugged filling orifice it) for introduction of the body of primary cooling liquid 9. A secondary cooler is provided in the form of a copper cooling coil 6 having inlet and outlets 7 and 8 extending through -a sidewall of casing 3 for connection with a liquid circulating system, the coil 6 being arranged coaxially in casing 3 around the heated surface 4 and radially spaced from it. An expansible damping member is provided in the form of an annular or toroidal element 20 made of flexible material and partly inflated with gas, e.g. air, at an initial pressure somewhat less than the prescribed operating pressure in the liquid 9. The toroidal damper 20 is arranged around the heated body 1 in the space between it and the cooling coil 6. Further, an annular deflector baffle 21 is shown positioned in the annular space between the outer surface of body 1 and the toroidal element 20, being supported in position through any suitable means, not shown, preferably from the wall of casing 3. The baffle 21 serves to hold the toroidal damper member 20 in position and prevent it from coming onto contact with the heated surface while allowing it to contract and expand. The annular baffle 21 has outturned end flanges 22 to contribute to retain the damping member 20 in position. The annular deflector or baffle also serves to promote convection movement of the liquid 9 by creating a thermosyphon effect whereby the heated liquid adjacent to the heat-dissipating protuberances 5' rises along the inner surface of the baffle 21 and the cooler liquid adjacent the cooling coil 6 descends along the outer side of the baffle. Such convection movement promotes the rapid recondensation of the large vapor bubbles in the subcooled liquid.

It will be understood that in a non-isotherm surface boiling evaporation cooler according to the invention, the subcoolin g of the evaporated liquid required to ensure surface boiling, may be accomplished by means other than the provision of a cooling coil in which a secondary cooling fluid is circulated. Thus, the subcool of the main body of liquid may be effected by cooling a wall portion of the boiler casing 3, at a sufliciently energetic rate, as by circulating a secondary cooling fluid in contact with the outer surface of such wall portion; and/or by providing cooling fins projecting from said outer surface into an airstream or the like.

The subcooling of the evaporating liquid may further be accomplished by circulating sa'id primary liquid 9 through the boiler enclosure. Such a form of embodiment of the invention is illustrated in FIG. 5. The general arrangement is similar to that of FIG. 4, except that the secondary cooling coil 6 and the associated secondary cooling fluid circulating system is here omitted. Instead, the boiler enclosure is provided with inlet and outlet means for circulating the main body of evaporating or primary liquid therein. As shown, the body 1 to be cooled, such as a combustion engine cylinder or electron tube casing, has heat-dissipating protuberances 5 formed on its external surface to provide the non-isotherm, temperature-stabilizing function in accordance with the applicants earlier patents as already described. An annular boiler casing 23 is sealingly secured around the heat dissipating surface portion 4 of the part 1 being cooled, and includes a lower domed manifold section 25 and an upper manifold section 28. An inlet 24 connects with manifold section 25 and an outlet 29 connects with section 28, the inlet and outlet being connectable to a flow system, not shown, including a pump for circulating the primary cooling liquid through the boiler casing 23 at a sufliciently high rate to ensure that the desired subcooling of the liquid to an overall temperature below the normal boiling temperature of the liquid at the operating pressure used, as required for the surface boiling effect described herein, is ensured. A toroidal damping element 20 made of suitable natural or synthetic rubberlike sheet material partially inflated with gas, e.g. air, is positioned in casing 23 around the heated surface 4, and is retained in position in spaced relation around said surface by an annular separator or baflie plate 26, supported through means not shown from the wall of casing 23. The baflie plate 20 has an outturned radial lower flange 27 on which the base of annular damper 20 rests, being if desired loosely attached thereto by any suitable means as schematically indicated. Flange 27 preferably extends to the side wall of casing 23 in order to separate the damping member 20 from the inlet section ,of the liquid circulation path. As in the embodiment of FIG. 4, baflle plate 26 serves the additional function of promoting thermosyphon circulation of the liquid upward along its radially inner surface and downward along outer surface, thereby promoting recondensation of the vapor bubbles that form in contact with the hot wall 4. A grid-like member 30, made of wire or other suitable perforate member, is positioned across the upper end of the annular channel defined between the hot surface 4 and annular deflector baffle 20. The grid 30 acts to break up the large vapor bubbles as they issue from said upper end of said channel and promotes recondensation in contact with the cool liquid at the outer side of separator 20. It is found that with such an arrangement the sudden variations in pressure that tend to be created by the vaporization and recondensation of the liquid are substantially localized in the region of the grid-like member 30 and in the upper annular manifold section 28 immediately beyond it. These sudden pressure variations are effectively damped out by the expansions and contractions of the upper part of the toroidal inflated damping member 20 positioned around annular deflector 26. It will be noted that the lower end of the toroidal damper 20 is substantially screened off from the inlet manifold section 25 by the L-shaped flange 27 of the annular baffle 20.

In the modified embodiment shown in FIG. 6, the arrangement is very similar to that of FIG. 5 and will not be described in detail anew. In this case however, the perforate grid 30 is omitted, and instead the annular deflector baffle 26 is. formed with perforations 31 along its length. The annular baffle 26 is formed with L-shaped outturned flanges both at its upper and lower end with the lower flange separating damper 20 from the liquid inlet. The vapor bubbles forming around the non-isotherm high-temperature outer surface 4 of the part 1 to be heated, tend to be shot out radially outward from the heatdissipating protuberances 5 and/ or the intervening channels, are broken up through the perforations 31 and recondense in the cooler region of the liquid outside the annular baflle 26. In this process, sharp pressure fluctuations tend to be created which are effectively damped by the contractions and expansions of the toroidal semiinflated damper member 20 surrounding said annular bafile 26. and retained between the top and bottom flanges thereof.

In certain applications of the invention, the deformable damping means of the invention need not take the form of specially provided inflated members as above described, and the damping function may be accomplished by a suitable vapor chamber provided in the boiler, FIG. 7 illustrates one such embodiment of the invention, suitable for use in cases where the cooling structure is ensured of retaining a generally upright condition at all times in operation.

The structure shown comprises a tubular part 1 to be cooled, such as the outer anode or collector structure of a high-power electron tube, an internal combustion motor cylinder, or the like having a sealed upper end 34 and temperature-stabilizing protuberances 5-. A boiler chamber is defined around and above the part 1 by a disk-like base and a bell-shaped, domed casing 3 sealingly secured over said base and around part 1. An inlet for the cooling liquid is provided by a connection 24 at the lower part of the sidewall of bell casing 3. An outlet for said liquid is provided in the form of a vertical riser pipe 29 extending upward through an opening in the top of said bell 3, and having a flared open lower end 33 overlying the sealed top 34 of the part 1, at a slight vertical spacing thereabove. An annular deflect-or plate 26 is supported coaxially between the heated surface 4 and the sidewall of easing 3 and spaced from both walls. In operation, primary cooling liquid such as water is circulated at a relatively high rate through the inlet 24 into the boiler chamber and out through the upper outlet 29 from and to a conventional circulating system not shown. When the inner surface of the tubular part 1 to be cooled is exposed to heat input as by electron bombardment, combustion of a gaseous mixture or other source depending on the nature of the part 1 to be cooled, stable temperature gradients are created along the sides of the protuberances 5 over the outer surface 4 -of the sidewall of part 1, with the highest temperatures existing at the roots of the protuberances. The liquid vaporizes in the immediate vicinity of said protuberances, and some of the bubbles burst so that vapor accumulates in the upper space 35 under the dome shaped top the boiler casing 3, which preferably is not subjected to substantial cooling. The free surface of the liquid becomes established at a certain :level 35 above the open lower end of the outlet pipe 29, and during the subsequent circulation of the liquid the amount of vapor in the upper space 32 does not increase. The vapor bubbles then rise along the inner surface of annular deflector 26 and recondense in the cooler liquid which tends to fall along the outer surface of the deflector, creating a convection circulation around the latter. The body of accumulated vapor in the upper space 32 is not involved in this circulation. It is noted that no substantial heat dissipation is produced from the sealed top 34 of the part 1. As the large vapor bubbles rise into the upper region of the body of Water above deflector 26 and recondense in the cooler liquid as just described, large fluctuations of pressure tend to occur. These pressure fluctuations cause contractions and exp-ansions of the eleastic body of vapor 32 in the top of the boiler, and are thereby damped. Thus, the cooling by surface boiling of the liquid in contact with the non-isotherm surface 4 can proceed smoothly and satisfactorily.

The simple embodiment of the invention just described with reference to FIG. 7, while suitable for certain applications, is open to the following difliculty. In cases where the rate of heat dissipation from the surface 1 is liable to vary greatly during operation, the free surface 35 of the liquid will undergo corresponding fluctuations and can at times drop a level below the outlet 33, whereupon the circulation of the liquid would be arrested. A modification of the invention in which this difliculty is eliminated is illustrated in FIG. 10. The general arrangement is similar to that of FIG. 7, except that the inlet pipe 24A instead :of opening into the hollow of the boiler 3 terminates at a level within the boiler corresponding to the desired average free level 35 for the body of liquid therein. Further, said inlet pipe 24A is shown as having a sealed end and as being formed with a plurality of small orifices 24B through its sidewall, such that the cool liquid will issue into the boiler space in a plurality of narrow, generally horizontally directed jets. The orifices 24B may have any desired shape, such as round holes or slots. With the arrangement described, should the free surface 35 of the liquid in the boiler become established at a level generally lower than that of the inlet orifices 243, the jets of cool liquid will issue into the free vapor space 32, creating an extremely energetic vapor-condensing action. The large amount of vapour thus condensed will tend to raise the level of liquid and immerse the inlets 248. With the inlets immersed the jets discharge into the body of liquid, and their vapour-condensing efficiency is greatly reduced, so that the liquid level tends not to rise any further. A self-regulating action is thus obtained which effectively stabilizes the average level of liquid and the average volume of the vapour pocket 32 at the desired values.

As earlier indicated, it is important that the heat dissipating surface is formed with structure that defines grooves or channels between heat-conductive extensions or protuberances which, in operation, will exhibit over their surfaces a non-isotherm pattern of temperature distribution encompassing the critical temperature, in order to create the stable temperature gradients which permit the attainment of high average temperatures over the surface without danger of burnout. Best results are obtained when said surface structures are proportioned in accordance with certain of applicants earlier teachings, which will now be summarized with reference to FIGS. 8 and 9. For fuller details, reference should be made to the applicants patent and copending patent application identified below.

FIG. 8 illustrates in cross section the shape of heat dissipating protuberances constructed in accordance with the applicants Patent No. 3,235,004. The protuberances 5 are in the form of parallel ridges or blocks of generally rectangular cross sectional shape separated by relatively narrow channels or grooves, preferably extending parallel to the generatrices of the generally cylindrical surface 4 of the tubular part 1 to :be cooled. The protuberances are proportioned so as to satify two conditions. The first condition is that the average width d of the intervening channels should be less than one third of their depth b d 1/ 312 The second condition involves the said channel depth b the transverse width a of the protuberances, and the heat conductivity factor 0 of the material from which the protuberances are made, and can be expressed by the formula b =m /ac where the geometrical dimensions a and [2 are expressed in centimeters, the heat conductivity c is expressed in Watts per centimeter and C, and m is a numerical factor in the range from 0.7 and 1.8.

FIG. 9 similarly illustrates the general shape of heat dissipating protuberances constructed in accordance with applicants co-pending patent application Ser. No. 512,090 filed Dec. 7, 1965. The protuberances 5 are here provided in the form of ridges or bosses having substantial contiguous bases and outwardly tapered over at least a substantial part of their total length k The construction should satisfy the following conditions:

where s and s are, respectively, the root area of the protuberance and the toal side area thereof c is the heat conductivity factor of the constituent material; q the critical value of the heat transfer flux density relating to the liquid used at the selected operating pressure, as indicated by tables available in the literature; 0 the specified temperature difference tolerated between the root and tip of a protuberance, i.e. the total extent of the temperaure gradient created along the side of a protuberance; the maximum value of the heat flux density per unit area of the heat input surface; k a numerical safety factor selectable in the range from 1 to 2; and p a numerical efficiency factor selectable in the range from 0.8 to 1.6. The above quantities can be expressed in any coherent system of units.

The invention, in that it combines the safe high operating temperature capability of the applicant's prior non-isotherm heat dissipating surfaces, as exemplified in FIGS. 8 and 9, with the benefits of surface boiling such as high flow velocity of a subcooled liquid under pressure and the high peak fluxes attainable therewith, makes possible greatly improved performance as compared to any earlier type of evaporation cooling system. The provision of the expansible elastic means for damping the sharp pressure fluctuations that would otherwise tend to occur with such a combination, enables attainment of heat dissipation fluxes two or more times higher than could be attained in a comparable system lacking the damping means of the invention without the appearance of unacceptable noise, impacts and cavitation.

As one example, a system of the type shown in FIG. 5 or 6 has been used to dissipate many hundreds of kilowatts power with a heat flux density of the order of l or 2 kilowatts per sq. cm. area, using as the cooling liquid distilled water circulated at a rate of about 0.35 liter per minute and per kilowatt dissipated heat. The resulting temperature elevation of the water was about 40 C., with an input temperature of 50 C., at the inlet 24 and a discharge temperature of 90 C. at the outlet 29. The pumping system used maintained a static pressure of somewhat more than 4 atmospheres within the boiler 3. At this pressure the saturation temperature of the water is about 140 C., and it is therefore seen that the water in such a system was subcooled to a temperature below the saturation temperature by an amount at no point less than 50 C. The system of the invention may .be operated with any suitable static pressure of the body of vaporizable liquid, a suitable pressure being two atmospheres or more.

What I claim is:

1. Heat transfer apparatus comprising:

a wall of heat conductive material having one side exposed to a source of heat; means defining an enclosure with the other side of the Wall and containing a body of a vaporizable liquid;

a set of heat dissipating extensions on said other side of the wall projecting into said liquid, said source of heat and said heat dissipating extensions being relatively dimensioned for non-isothermal heat transfer;

means for subcooling the liquid in operation to a temperature lower than the saturation temperature thereof at the pressure of said body of liquid whereby liquid will vaporize adjacent said heat dissipating extensions and the vapor will recondense in the subcooled liquid body; and

pressure shock absorption means in pressure-transmitting relation with said liquid in the enclosure; said pressure shock absorption means comprising prestressed elastic means adapted for elastic contraction and expansion in response to sudden pressure fiuctations created by said vaporization and recondensation effects whereby to contribute to the damping out of such fluctuations.

2. Apparatus according to claim 1, wherein said heat dissipating extensions and the intervening channels are so dimensioned as to verify substantially the relations d b/3 and b:m /ac, wherein d represents the average transverse width of an inter-extension channel, a the transverse Width of an extension between adjacent channels, c the heat conductivity factor of the wall material, and m a numerical coefficient within the range from about 0.7 to about 1.8, when a and b are expressed in centimeters and c in watts transmitted heat per centimeter and per degree centigrade.

3. Apparatus according to claim 1, wherein said heat dissipating extensions are so shaped as to have substantially contiguous bases and taper over at least a substantial part of their height, and are so dimensioned as to verify substantially the relations Where b represents the height of an extension, .9 and s the base area and total side surface area of an extension respectively, 0 the heat conductivity coefficient of the wall material, q the critical value of heat flux density of said liquid at the operating pressure, 0 a specified temperature drop from the base to the apex of an extension, p the maximum specified value of heat flux density per unit area of the heat input surface, It a numerical safety factor selectable over the range from 1 to 2, and p a nu merical efliciency factor selectable over the range from 0.8 to 1.6.

4. Apparatus according to claim 1 wherein said pressure shock absorption means comprises a closed balloonlike member pertially inflated with a gas.

5. Apparatus according to claim 1 wherein said pressure shock absorption means comprises means accumulating a substantial pocket of vapor of said liquid, vaporized by heat supplied by said heat dissipating extension subjected to said source of heat.

6. Heat transfer apparatus comprising:

a wall of heat conductive material having one side exposed to a source of heat;

means defining an enclosure with the other side of the wall and containing a body of a vaporizable liquid;

a set of heat dissipating protuberances on said other side of the wall and projecting into said liquid; said source of heat and said heat dissipating protuberances being relatively dimensioned for non-isothermal heat transfer;

means for subcooling the liquid in operation to a temperature lower than the saturation temperature thereof at the pressure of said body whereby liquid vaporizing adjacent said heat dissipating protuberances will recondense in the subcooled liquid body;

and pressure shock absorption means comprising flexible sealing means having one side exposed to the liquid in the enclosure and a body of gas on the other side of said sealing means, said body of gas being at a pressure such as to be capable of elastic contraction and expansion in response to sudden pressure fluctuations created by said vaporization and recondensation eflects whereby to contribute to the damping-out of such fluctuations.

7. Apparatus according to claim 6, wherein said flexible sealing means constitutes at least one closed balloonlike member partially inflated with said gas.

8. Apparatus according to claim 7, including means for retaining said member in a part of the enclosure spaced from said heat dissipating well while not interfering with the elastic contraction and expansion of the member.

9. Apparatus according to claim 7, wherein said enclosure includes a section detachably connected with a main section of the enclosure, and means are provided for retaining said member in said detachably connected section while not interfering with the elastic contraction and expansion of the member.

10. Apparatus according to claim 7, wherein said enclosure surrounds a circumferential surface of said heat dissipating wall, and said balloon-like member is of generally toroidal shape and surrounds said circumferential wall surface.

11. Apparatus according to claim 6, wherein said flexible sealing means constitutes a diaphragm, and means mounting said diaphragm to seal off a surface portion of said body of liquid from said gas.

12. Apparatus according to claim 11, wherein said enclosure includes a first section detachably connected with a main enclosure section, a second section detachably connected with said first detachable section and containing said body of gas, and said diaphragm is mounted between said first and second detachable sections so as to seal olf the liquid in said main enclosure section from gas in said second detachable section.

13. Apparatus according to claim 6, including means for circulating said liquid through the enclosure, means defining a circulation path through the enclosure from a liquid inlet past said heat dissipating wall surface to a liquid outlet, separating means for defining a liquid inlet compartment and a liquid outlet compartment in the enclosure, and said flexible sealing means is arranged to be freely exposed to the liquid in said outlet compartment while being substantially isolated from said inlet compartment by said separating means.

14. Apparatus according to claim 6, including means for circulating said liquid through the enclosure, means defining a circulation path through the enclosure from a liquid inlet past said heat dissipating surface to a liquid outlet, and including deflector means for channelizing to flow of liquid past said heat dissipating surface in a relatively narrow hot region adjacent thereto from said inlet towards said outlet whereby to define a relatively cooler region in said liquid body on the side of said deflector means remote from said surface, and wherein said flexible sealing means is arranged to be exposed to said relatively cooler region.

15. Apparatus according to claim 14, including gridlike structure positioned across the end of said narrow region adjacent the heat dissipating surface directed towards said liquid outlet.

16. Apparatus according to claim 14, wherein said deflector means is perforate.

17. Heat transfer apparatus comprising:

a wall of heat conductive material having one side exposed to a source of heat;

means defining an enclosure with the other side of the wall and containing a body of a vaporizable liquid;

a set of heat dissipating extensions on said other side of the wall and projecting into said liquid, said source of heat and said heat dissipating extensions being relatively dimensioned for non-isothermal heat transfer;

means for subcooling the liquid in operation to a temperature lower than the saturation temperature thereof at the pressure of said body whereby liquid vaporizing adjacent said heat dissipating extensions will recondense in the subcooled liquid body; and

means for accumulating a substantial pocket of vapor of said liquid in an upper part of said enclosure in the operation of said apparatus, whereby said vapor pocket will be adapted for elastic contraction and expansion in response to sudden pressure fluctuations caused by said vaporization and recondensation ef fects, whereby to contribute to damping said pressure fluctuations.

18. Apparatus according to claim 17, including means for circulating said liquid through the enclosure, means defining a circulation path through the enclosure past said heat dissipating wall surface and including a liquid inlet connected with said enclosure, and a liquid outlet comprising a riser pipe having its lower end opening at an elevation in the enclosure substantially below the upper end of said enclosure whereby to permit accumulation of said vapor pocket in operation.

19. Apparatus according to claim '17, including means for circulating said liquid through the enclosure, means defining a circulation path through the enclosure past said heat dissipating wall surface and including a liquid inlet and a liquid outlet, said liquid outlet comprising a riser pipe having its lower end opening at an elevation in the enclosure substantially below the upper end of said enclosure whereby to permit accumulation of said vapor pocket in operation, and said liquid inlet comprising orifice means positioned and arranged for discharging at least one narrow laterally-directed liquid jet into the enclosure at an elevation somewhat above the elevation at which said riser pipe opens, whereby the elevation of said inlet jet will substantially determine the average elevalion of the free surface of the liquid body in the enclosure and the volume capacity of said vapor pocket.

References Cited UNITED STATES PATENTS 2,777,009 1/1957 Whitman 174-15 2,882,449 4/ 1959 Beurtheret -74 X 2,961,476 11/1960 Maslin et a1. 174-15 2,984,773 5/1961 Guldemond et al. 317234 3,043,900 7/1962 Reisinger 174-l5 X 3,293,349 12/1966 Diebold et al. 17415 X ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner. 

